Info - Automatic Air Conditioning Control Operation

This bulletin is being revised to update the model years and add HUMMER. Please discard Corporate Bulletin Number 99-01-39-007A (Section 01 -- HVAC).

Automatic air conditioning functional description: Vehicles with automatic air conditioning (single and dual zone) have both automatic and manual operating systems.

For the system to operate automatically, the system controls must meet the following criteria:

1. The temperature setting must be one step warmer than the coldest allowable setting.
2. The temperature setting must be one step cooler than the warmest allowable setting.
3. The fan speed selector must be in the automatic position, no driver input to lower or raise the blower speed, after the auto button or key pad has been pushed.
4. The air flow selector must be in the automatic position, no driver input to change the air flow output, after the auto button or key pad has been pushed.

If these conditions are not met, the system is considered in the manual mode.

1. In the manual mode, all indicators of automatic operation (i.e. lights, messages, etc., depending on the vehicle car line) will be off.
2. Manual mode is when the driver air conditioning controls are in the full hot, full cold, non-automatic blower speed or non-automatic air distribution control positions.

Do not replace air conditioning controls, as the system is functioning as designed.